CLIMATE CHANGE EFFECTS ON SEAGRASSES, MACROALGAE AND THEIR ECOSYSTEMS: ELEVATED DIC, TEMPERATURE, OA AND THEIR INTERACTIONS

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1 CLIMATE CHANGE EFFECTS ON SEAGRASSES, MACROALGAE AND THEIR ECOSYSTEMS: ELEVATED DIC, TEMPERATURE, OA AND THEIR INTERACTIONS Marguerite S. Koch, George E. Bowes, Cliff Ross, XingHai Zhang Josh Filina, Kate Peach, Brent Anderson Aquatic Plant Ecology Laboratory, Biological Sciences Department, Florida Atlantic University Department of Biology, University of Florida Department of Biology, University of North Florida

2 Why are Marine Macroalgae & Seagrasses Important? Habitat Foundation Base Foodwebs Sediment Stabilization Sediment Generation Tropics Settlement Sites Corals Nutrient Cycling Competitors (Nuisance spp) Substrates Epiphytes

3 Outline Talk I. REVIEW i. INORGANIC C SPECIATION ii. iii. iv. CARBON LIMITATION ISSUES MECHANISMS CACQUISITION CASCADING EFFECTS OA CLIMATE CHANGE II. EXPERIMENTAL RESEARCH CO 2 X TEMP INTERACTION

4 Inorganic Carbon Speciation Carbonate Equilibria (modified from Fabry et al. 2008)

5 Review Marine Macroautotroph s InorganicC Pathways, Bicarb Use and Ci Saturation Primarily C 3 species (>85%) All use HCO 3 (>99%) External Carbonic Anhydrase (CA ext ) Not saturated present [Ci] Review Climate Change and OA Effects on Marine Macroautotrophs Koch, Bowes, Zang, and Ross (in press Global Change Biology)

6 Carboxylation vs Oxygenation C 3 Plants (Problem CO 2 Affinity and Photorespiration) Carboxylation (Calvin Cycle) Oxygenation C lost not recycled up to 50% loss C No ATP produced and loss ATP and NADPH Increase in temperature results > photorespiration

7 Carbon Concentration Mechanisms (CCMs) C 4 /HCO 3 (Adaptation to Low CO 2 Concentrate CO 2 at Rubisco) C 4 or C 4 Like (Single Cell) Cytoplasm Bicarbonate Uptake (CCM?) H ATPase pumpco 2 pump 4 H CO 2 2 ATPase 3 Pump? 5 1 Chloroplast C 4 Radakovits et al. (2012) 1. C 3 pathway and depend on CO 2 diffusion 2. H Pump to lower ph cell surface speed up hydrolysis reaction CA at Ocean ph 3. Potentially a CO 2 pump 4. Bicarbonate Transporter intercellular CA

8 Photosynthesis (mg O 2 g 1 dry wt h 1 ) Seagrasses and Marine Macroalgae Utilize HCO 3 and CO 2 Are They Saturated with Ci? 8 6 DIC Ocean ~2.4 mm ph 7.80 ph ph Not DIC Saturated Higher P elevated CO 2 Can utilize HCO Dissolved inorganic carbon (mm) Durako 1993 Thalassia testudinum (Seagrass Angiosperm)

9 Ocean Acidification and Climate Change Effects on Tropical Macroalgae and Seagrass Atmosphere Ocean Dissolution Nutrient Cycling Ω CaCO3 Calcification CA CO 2 3 ph CO 2(aq) HCO 3 Temp CCM C 4 / HCO 3 Use 0/ CO 2(atm) No CCM C 3 Photosynthesis Growth Biomass H Rubisco Downregulation 0/ C:N:P Herbivory Photorespiration Respiration Antiherbivory Metabolites Temp Cellular Stress Response System Thermal Threshold Competition Competition Competition Life History Life History Life History Calcifiers Fleshy Seagrass Cyanobacteria

10 Experimental Mesocosms (OA x Temp)

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12 Experimental Design Amb pco 2 x Amb Temp High pco 2 x Amb Temp Amb pco 2 x High Temp High pco 2 x High Temp Feb 2012/ July 2011 Tank Avg (SE) n=6 Ambient High Treatment Temperature ( o C) 24.8 / / oc ph 7.99/ / ph CO 2 (mmol kg 1 ) 13/11 25/25 108% increase

13 Photosynthesis Measurements (P:I curves) OxyLab 3 11 Light levels 0, 25, 50, 75, 100, 200, 400, 600, 800, 1000 and 1,200 mmol m 2 s 1

14 Elevated pco 2 x Temperature Winter Experiment Sargassum fluitans 200 Halimeda incrassata High Temp High CO Control n mol O2 gwwt 1 min High CO 2 x Temp High Temp High CO 2 x Temp High Temp High Temp (28 oc) Control (24 oc) High CO2 (1000 uatm) Control (400 uatm) High CO 2 High CO PAR PAR

15 Summer 2011 High CO2 Sargassum fluitans Halimeda incrassata Pmax (% Change from Controls) High Temp (34 oc) 32 Winter 2012 CATH CHTA CHTH High Temp (28 oc) High CO2 High Temp High CO High Temp High CO2 40

16 Conclusions Ocean acidification (OA) effects on marine macroautotrophs: Increased CO 2 for C 3 spp not able to employ CCMs Increase rate of dehydration of HCO 3 by external Carbonic Anydrase (CA ext ) Lower CO 3 2 and saturation states CaCO 3 Potentially uncouple photosynthesiscalcification reactions (calcifiers) Elevated CO 2 and temperature (4 o C) stimulates photosynthesis below thermal limits Thermal stress creates a negative synergy between elevated Temp x CO 2 Calcifying species unlikely to respond to CO 2 constrained low CaCO 3 saturation states Competition with fleshy species may also reduce calcified algae

17 Future Research Needs Basic research on photosynthetic biochemistry and calcification mechanisms and their responses to CO 2 and Temperature The effect of OA on CCMs and facultative use of various DIC acquisition systems The role of temperature and light on DIC limitation and acquisition systems employed Thermal limits of tropical species under climate change Shortterm physiological responses need to be linked to longerterm growth experiments in the mesocosm and field and interactions at the community

18 Acknowledgements We sincerely thank Chris Langdon/Frank Millero pco 2 measurements Students laboratory/field/ review assistance FAU Climate Change Initiative Everglades National Park

19 Questions?